1. Field of the Invention
The present invention relates to improvements in a pressure control device for hydraulic braking system of an automotive vehicle, and more particularly to a hydraulic pressure control device for an anti-lock braking control and a slippage control in acceleration.
2. Description of the Prior Art
Japanese Patent Provisional Publication No. 58-122246 discloses a typical pressure control device applied to a hydraulic braking system which carries out the anti-lock braking control and the slippage control in acceleration. This device includes a pressure control valve which is disposed to a main passage communicating a master cylinder and a wheel cylinder in order to control a hydraulic pressure of the wheel cylinder. For carrying out the anti-lock braking control, the hydraulic fluid in the wheel cylinder is lowered in pressure by draining it to a storage chamber through the pressure control valve, and is fed to the main passage between the pressure control valve and pressure source switching valve. During the slippage in acceleration, in order to suppress the slippage of the wheels, this system operates to temporarily store a hydraulic pressure in the storage chamber through a supply pump, to stop the communication between the master cylinder and the pressure control valve, and to communicate the accumulator and the pressure control valve for supplying the hydraulic pressure of the accumulator to the wheel cylinder.
However, the conventional pressure control device performs to operate the return pump even during the slippage control in acceleration. This operation of the return pump generates noises which make passengers uncomfortable.